The following relates to data delivery and encoding methods pertaining to pattern specification and rendering in display and printing devices. It finds particular application to distributing super-resolution encoding (SRE) “codes” among groups of pixels, forming a “super cell” for SRE specification which allows for a greater number of bits and therefore patterns to be used in a code specification.
Super-resolution encoding (SRE) refers to a rendering mode whereby a set of high resolution binary patterns can be generated from a lower resolution “code”. In contrast to standard halftoning, where the binary pattern generated is dependent on the (s,f) position relative to the halftone dot cell, SRE is not spatially dependent, and allows for a maximum of 2N unique rendering patterns for the associated sub-pixels, where N is the number of bits used to represent the code space. For N=8 bits, there is a total of 256 possible codes (and therefore patterns) that can be specified. SRE can be effective for improved rendering of text and line art, where edge accuracy is of particular importance. Certain printer devices allow for 2400×2400×1 SRE rendering, for example the Xerox DC8000, whereby each 600×600 dpi (8 bit) pixel is used to render a 4×4 binary pattern. In this case, there are 2^16 possible patterns; however, only two hundred and fifty six are accessible due to the eight bit code limitation. For simple edge rendering applications, the two hundred and fifty six pattern space is usually sufficient to handle most cases of interest. On the other hand, for applications that use the SRE approach in more sophisticated ways, such as SRE halftoning (U.S. patent application Ser. Nos. 11/443,016 and 11/443,351), two hundred and fifty six patterns may be insufficient. In those cases substitution of the “next best” pattern is required, leading to sub-optimal rendering.
Zeck et al. (U.S. Pat. No. 6,020,979) describes a method to encode high resolution rendering patterns using eight bit codes specified at a lower resolution, known as “Super Resolution Encoding” (SRE). In contrast to standard halftoning, where the binary pattern generated depends on the contone level and the raster position relative to the halftone dot cell, SRE produces fixed patterns that are only dependent on the N-bit code specified.
Some Xerox printers support super resolution encoding/decoding. When a particular pixel tag (tag=3 for example) is passed, the SRE mode is activated for that pixel, and the contone data for that pixel is interpreted as a rendering code. There are 256 possible SRE codes, each of which will result in a different 4×4 bit pattern to be rendered. Therefore, a single 600×600 dpi 8 bit pixel can specify a 2400×2400 dpi binary rendering pattern.
FIG. 1 illustrates several examples of SRE patterns 102, 104, 106, 108, and 110 and their corresponding SRE codes. As illustrated, each SRE code is associated with a grid that is four bits wide by four bits high. The grid has one or more bits that are completely filled or not filled at all. In this embodiment, the bits are square shaped. However, it is to be appreciated that the bits can be substantially any shape used to tile a plane, such as rectangles, hexagons, etc.
The bit patterns 102-110 are four bits wide by four bits high, such that there are sixteen bits in each pattern. The bits are square shaped and the entire grid has a square shape. It is to be appreciated, however, that the grid can have substantially any shape. Each pattern has a corresponding SRE code. In one example, bit pattern 110 has fifteen bits in the upper left hand corner that are completely filled wherein the lower right bit is not filled. This exemplary bit pattern is associated with SRE code 254. Substantially any pattern can be associated with substantially any SRE code.
There are 216 (65,536) possible patterns for the 4×4 cell, although only 256 of these can be addressed due to the 8 bit code limitation. Such capability can improve the rendering of edges, corners, when used in conjunction with techniques such as anti-aliasing. In these simple applications, the 8 bit code limit is generally sufficient to produce the necessary patterns for improved edge-rendering.
U.S. patent application Ser. Nos. 11/443,016 and 11/443,351 propose a method whereby the SRE patterns are used as building blocks to construct high resolution halftones using low resolution code descriptions. In this approach, it was shown that high resolution dots (e.g., 2400×2400) could be well approximated using the two hundred and fifty six patterns available. For certain simple halftone dot geometries, such as 0 or 45 degree mono designs, the halftone can be exactly described in terms of the available SRE patterns. For more complex dots, however, pattern substitution is necessary, where the “next best” SRE pattern is chosen to approximate the actual pattern that would be rendered with the true 2400×2400 halftone dot. In these cases, sub-optimal rendering will occur, possibly resulting in objectionable artifacts such as contouring or moiré. What are needed are processes and/or systems that overcome these and other shortcomings associated with the representation of SRE patterns.